Plasma processing apparatus

ABSTRACT

In the plasma processing apparatus of the present invention, a first electrode for connecting a high frequency electric power source in a chamber is arranged to be opposed to a second electrode. A substrate (W) to be processed is placed between the electrodes. There is provided a harmonic absorbing member for being able to absorb harmonics of the high frequency electric power source so as to come in contact with a peripheral portion or circumference of a face of the first electrode  21 , which is opposite the second electrode. The harmonic absorbing member absorbs the reflected harmonic before the harmonic returns to the high frequency electric power source. By absorbing the harmonic in this manner, the standing wave due to the harmonic will be effectively prevented from being generated, and the density of plasma is made even.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims the benefit of U.S.application Ser. No. 09/959,745, filed Nov. 5, 2001, which is a NationalStage application of PCT/JP00/02770, filed Apr. 27, 2000, and claimspriority to Japanese Patent Application Nos. 11-125637, filed May 6,1999; 11-126878, filed May 7, 1999; 11-129696, filed May 11, 1999 and11-141209, filed May 21, 1999. The entire content of each of theseapplications is incorporated herein by reference to the extent that suchincorporation does not create an issue of new matter.

TECHNICAL FIELD

The present invention relates to a plasma processing apparatus forperforming etching and film forming on a substrate such as asemiconductor substrate by plasma processing.

BACKGROUND ART

In a process for manufacturing semiconductor devices, various plasmaprocessing such as etching, film forming by sputtering or CVD filmforming (Chemical Vapor Depositing) have been frequently employed.

There have been known various types of plasma processing apparatuses,among which a capacitive coupling type parallel plate plasma processingapparatus is the apparatus the most popularly distributed and used.

This type of plasma processing apparatus has a pair of parallel flatplate electrodes (upper and lower electrodes) in a reduced-pressurechamber. A semiconductor wafer to be processed is placed between theelectrodes, then process gas (treatment gas) is introduced into thechamber and electric power with high frequency is applied to one of theelectrodes. A high frequency electric field generated between theelectrodes generates plasma from the process gas to perform plasmaprocessing on the semiconductor wafer.

In etching an oxide film or the like formed on a semiconductor waferwith use of such a plasma processing apparatus, the pressure in thechamber is set at an intermediate level to generate plasma having anintermediate density, thereby the optimum radical control can beattained. In such a condition, the optimum plasma can be obtained torealize etching with good stability and reproducibility at a highselective ratio.

In accordance with the downsizing of a device, however, the request forthe ultra-integration of a circuit is increased. There are also designrule constraints on features like the contact hole. The contact hole isrequired to be thin and deep, i.e., to have higher aspect ratio. Theconventional oxide film etching method is, therefore, beginning to benot good enough to satisfy the demands of the market.

To cope with such recent requests, the frequency of the electric powerapplied to the electrode is set at a higher level to generate plasmahaving a higher density, so as to maintain good dissociation. Bygenerating the plasma in such a manner, suitable plasma can be generatedin a lower pressure, and thus the device with a smaller design rule canbe manufactured.

With the conventional plasma processing apparatus, however, the upperelectrode is formed from a conductor or semiconductor. Therefore, whenthe frequency of the electric power applied to the upper electrode isset at a high level, the inductance on the surface of the electrode willbe increased so as not to be neglected, whereby the electric field inthe opposite direction will be uneven.

Further, such a higher density of the plasma by the higher frequencyremarkably causes non-linear characteristics of the plasma, so that aharmonic may be easily interposed on the reflected wave form the plasma.Particularly, with use of the electrode having a diameter of 250 to 300mm, it has been found from experience that such a harmonic generates astanding wave on the surface of the electrode, which makes the electricfield on the surface of the electrode uneven.

If the electric field is made uneven in such a manner, the density ofplasma will be also made uneven, with the result that the etching rateof etching will be uneven. Accordingly, it is essential to make theetching rate even by eliminating the causes of the uneven electricfield.

The above-mentioned problems in generating a high-density plasma,however, have not been recognized clearly, and thus a proposal forpreventing the above-mentioned uneven electric field has notsufficiently been presented yet.

Further, according to the conventional plasma processing apparatus, theelectric power is applied to the upper electrode with use of an electricpower applying rod, and thus a box having a size substantially equal toa chamber encloses the electric power applying rod to shieldelectromagnetic wave.

However, since the inductance of the electric power applying rod is veryhigh, if the frequency of the high frequency power supplied to the upperelectrode is set at a higher level in order to increase the plasmadensity, the harmonic of the wave reflected from the plasma is reflecteddue to the inductance component of the electric power applying rod.Further, reflection is caused at every portions within the box in whichthe electric power applying is disposed, and the resultant reflectedharmonic backs to the surface of the upper electrode exposed to theplasma.

With the electrode having a diameter of 250 mm to 300 mm, a standingwave will be easily generated on the surface of the electrode due to thehigher harmonic (higher harmonic), which makes the electric field on thesurface of the electrode uneven.

The electric power applying rod is provided to the center of the upperelectrode on the rear surface thereof. When the frequency of theelectric power applied to the electrode is increased to generatehigh-density plasma, the high frequency current flows only on thesurface of the electrode. The high frequency electric power applied fromthe electric power applying rod to the upper electrode flows through therear surface of the electrode to the outer periphery of the roundelectrode to be supplied from the outer periphery to the center of theelectrode.

The outer periphery of the electrode is enclosed by an insulator(capacity component) and the chamber enclosing the insulator isgrounded. With this structure, the standing wave is generated on theplasma contacting face of the upper electrode by the interference, whichmakes the electric field on the electrode in the direction of thediameter uneven. The unevenness of the electric field also makes thedensity of the plasma uneven, which causes an uneven etching rate.Accordingly, these causes need to be eliminated to make the etching rateeven.

However, as mentioned before, the problems in generating thehigh-density plasma, have not been recognized clearly, and thus aproposal for preventing the above-mentioned uneven electric field hasnot been sufficiently presented yet.

DISCLOSURE OF INVENTION

The present invention is intended to provide a plasma processingapparatus capable of making the density of plasma even by suppressingthe unevenness of the electric field on the surface of an electrode inthe plasma processing using high-density plasma with use of which adevice can be formed finer.

In order to attain the above-mentioned object, the present inventionprovides a plasma processing apparatus comprising a chamber containing asubstrate to be processed; a first electrode and a second electrodearranged to be opposed to each other in the chamber; high frequencyelectric power applying means for applying high frequency electric powerto the first electrode; a harmonic absorbing member arranged to comeinto contact with one of an outer periphery and an outer peripheral faceon an opposing face (on which the first electrode faces the secondelectrode) of the first electrode being opposed to the second electrode,for absorbing a harmonic generated by the high frequency electric powerapplied by the high frequency electric power applying means; exhaustmeans for exhausting the chamber to maintain a pressure in the chamberat a reduced level; and process gas introducing means for introducingprocess gas into the chamber, wherein in a state that one of the firstand second electrodes is caused to hold the substrate to be processed,while the harmonic absorbing member absorbs the harmonic generated bythe high frequency electric power, a high frequency electric field isformed between the first and the second electrodes to generate plasma ofthe process gas, and the substrate to be processed is subjected toplasma processing with the plasma while the harmonic absorbing memberabsorbs the harmonic generated by the high frequency electric power.

In the plasma processing apparatus of the present invention, highfrequency electric power is applied to the first electrode. There isprovided a harmonic absorbing member for absorbing a harmonic of thehigh frequency electric power source so as to come into contact with aperipheral portion or circumference of a face of the first electrode,which is opposite to the second electrode. The harmonic absorbing memberabsorbs a harmonic reflected from plasma before the harmonic returns tothe high frequency electric power source. By absorbing the harmonic inthis manner, the standing wave due to the harmonic will be effectivelyprevented from being generated, and the density of plasma is made even.With such a structure, the standing wave due to the harmonic can beprevented to suppress the unevenness of the electric field on thesurface of the electrode due to the standing wave, with the result thatthe density of plasma can be made even.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view showing the plasma etching apparatusaccording to the first embodiment of the present invention.

FIG. 2 is a schematic view for explaining the cause of the standing waveformed on the electrode applied with a high frequency wave.

FIG. 3 is a sectional view showing an example of an arrangement of ahigh frequency wave absorbing member.

FIG. 4 is a graph showing frequency characteristics of return loss whena ferrite sinter having a thickness of 7 mm is used as the highfrequency wave absorbing member.

FIG. 5 is a graph showing frequency characteristics of return loss whena ferrite sinter having a thickness of 4.5 mm is used as the highfrequency wave absorbing member.

FIG. 6 is a sectional view showing the plasma etching apparatusaccording to the second embodiment of the present invention.

FIG. 7 is a sectional view schematically showing the supply path of thehigh frequency electric power on the electrode.

FIG. 8 is a bottom view schematically showing the supply path of thehigh frequency electric power on the electrode.

FIG. 9 is a sectional view schematically showing a first example of theupper electrode according to the second embodiment of the presentinvention.

FIG. 10 is a sectional view schematically showing a second example ofthe upper electrode according to the second embodiment of the presentinvention.

FIG. 11 is a sectional view schematically showing a supply path of thehigh frequency electric power in the second example of the upperelectrode according to the second embodiment of the present invention.

FIG. 12 is a sectional view schematically showing a third example of theupper electrode according to the second embodiment of the presentinvention.

FIG. 13 is a sectional view schematically showing a fourth example ofthe upper electrode according to the second embodiment of the presentinvention.

FIG. 14 is a sectional view schematically showing a fifth example of theupper electrode according to the second embodiment of the presentinvention.

FIG. 15 is a sectional view schematically showing a sixth example of theupper electrode according to the second embodiment of the presentinvention.

FIG. 16 is a sectional view showing the plasma etching apparatusaccording to the third embodiment of the present invention.

FIGS. 17A and 17B are schematic views for explaining the principle ofthe third embodiment of the present invention.

FIG. 18 is a sectional view showing the plasma etching apparatusaccording to the fourth embodiment of the present invention.

FIG. 19 is a sectional view showing the plasma etching apparatusaccording to the fifth embodiment of the present invention.

FIG. 20 is a circuit diagram showing an equivalent circuit of anelectric power supplying rod and a cylindrical conductive member in theplasma etching apparatus according to the fifth embodiment of thepresent invention.

FIG. 21 is a circuit diagram showing an equivalent circuit of an uppersurface of the upper electrode (electrode supporting body) and aplate-like conductive member in the plasma etching apparatus accordingto the fifth embodiment of the present invention.

FIG. 22 is a sectional view showing the plasma etching apparatusaccording to the sixth embodiment of the present invention.

BEST MODE FOR CARRYING OUT OF THE INVENTION

The present invention can be more fully understood from the followingdetailed description of embodiments of the invention in conjunction withthe accompanying drawings.

FIG. 1 is a sectional view schematically showing the plasma etchingapparatus according to the first embodiment of the present invention.

A plasma processing apparatus 1 is constituted as a capacitive couplingtype parallel plate etching apparatus having two electrode plates beingopposed to each other (arranged in parallel and facing each other) oneof which is connected to a plasma generating electric power source.

The plasma processing apparatus 1 has a chamber 2 formed of aluminum ina cylinder shape the surface of which is processed (subjected to ananodic oxidation process) to form alumite. The chamber 2 is grounded.

The chamber 2 is provided on the bottom face with an insulator 3, suchas a ceramic, upon which a suscepter supporting body 4 formed in asubstantially columnar shape is placed, for mounting an object to beprocessed, such as a semiconductor wafer (hereinafter referred to as“wafer”) W. There is further provided on the suscepter supporting body 4a suscepter 5 constituting a lower electrode. The suscepter 5 isconnected to a high-pass filter (HPF) 6.

The suscepter supporting body 4 contains a refrigerant passage 7 intowhich a refrigerant such as liquid nitrogen is introduced through arefrigerant pipe 8 and circulates therein. The coldness of therefrigerant is transmitted to the wafer W via the suscepter 5 to controlthe surface of the wafer W which is to be processed at a desiredtemperature.

The suscepter 5 is formed in a disk-like shape the center of the upperside of which protrudes upwards, and mounts the wafer W and anelectrostatic chuck 11. The electrostatic chuck 11 has an electrode 12implanted in the body formed of an insulator, and electrostaticallyholds the wafer W with use of the Coulomb force or the like when theelectrode 12 is applied with a direct voltage of 1.5 kV, for example, bya direct voltage source 13.

The insulating plate 3, the suscepter supporting body 4, the suscepter5, and the electrostatic chuck 11 is provided with a gas path 14 forsupplying a temperature transmission medium such as He gas to the rearsurface of the wafer W, via which the coldness of the suscepter 5 istransmitted to the wafer W to control the wafer W at a predeterminedtemperature. The suscepter 5 is provided on the outer periphery of theupper surface with a circular focus ring 15 to surround the wafer Wmounted on the electrostatic chuck 11. The focus ring 15 is formed of aconductive material such as silicon and facilitates even etching of thewafer.

The suscepter 5 functions as the lower electrode. There is provided anupper electrode 21 above and opposite the suscepter 5.

The faces of the suscepter 5 and the upper electrode 21 which face eachother are referred to as “opposing faces” hereinafter. The faces notbeing opposed to each other are referred to as non-opposing faces.

The opposing face of the upper electrode 21 is formed as an electrodeplate 23 having a number of delivery holes 24. The electrode plate 23 isfixed to an electrode supporting body 22. The body 22 is a water-cooledstructure formed from a conductive material such as aluminum the surfaceof which has been processed to form alumite. The upper electrode 21according the embodiments to be described below is comprised by theelectrode plate 23 and the electrode supporting body 22.

The outer periphery of the upper electrode 21 is provided withinsulating member 25 formed in a ring-like shape to be placed therein.

There is provided a harmonic absorbing member 51 formed in a ring-shapeso as to come in contact with the outer peripheries of the electrodeplate 23 and the insulating member 25. There is also provided aninsulating member 52 formed in a ring-shape so as to bridge theelectrode plate 23 and the insulating member 25 and cover the harmonicabsorbing member 51.

With this structure, the upper electrode 21 is fixed to on the chamber 2to be put into the insulating material 52. The suscepter 5 is separatedfrom the upper electrode 21 by around 10 to 60 mm.

The harmonic absorbing member 51 is designed to absorb or attenuate theharmonic generated by the high frequency electric power reflected byplasma by using the magnetic resonance loss effect. As a materialabsorbing the harmonic, ferrite is well-known, and thus the harmonicabsorbing member 51 is formed of a material containing ferrite. Byvarying the thickness and the material of the harmonic absorbing member51, the frequency band of the harmonic to be absorbed can be adjusted.

On the other hand, the frequency band of the harmonic to be absorbed canbe widened by forming the harmonic absorbing member 51 of laminatedmaterials having different frequency characteristics. In this manner, astanding wave can be prevented by absorbing and attenuating the harmonichaving the desired frequency.

The electrode supporting body 22 of the upper electrode 21 is providedwith a gas inlet 26 connected to a gas supplying pipe 27. The gassupplying pipe 27 is connected to a process gas source 30 via a valve 28and a mass flow controller 29. The process gas source 30 suppliesprocess gas for plasma processing such as etching.

The gas conventionally employed in the plasma processing can be employedas the process gas. It is preferable to employ gas containing elementsof the halogen series, such as fluorocarbon gas (CxFy) orhydrofluorocarbon gas (CpHqFr). The rare gas such as Ar, He, and thelike and N₂ can be added, of course. The bottom portion of chamber 2 isprovided with an exhaust pipe 31 connected to an exhaust system 35. Theexhaust system 35 has a vacuum pump such as a turbo molecule pump whichcan reduce the pressure in the chamber 2 to a predetermined pressuresuch as 1 Pa or less.

The chamber 2 is provided with a gate valve 32 on a sidewall. When thegate valve 32 is opened, the wafer W is conveyed to/from a load lockchamber (not shown) adjacent to the chamber 2.

The upper electrode 21 is connected to a high frequency electric powersource 40 for generating plasma via a matching device 41. The electricpower from the high frequency electric power source 40 is supplied tothe upper electrode 21 via an electric power supplying rod 33.

The upper electrode 21 is connected to a low pass filter (LPF) 42. Thehigh frequency electric power source 40 supplies electric power having afrequency of 27 MHz or higher. By applying electric power having such ahigh frequency, a high density plasma can be generated so as to maintainthe chamber 2 at a good dissociation condition to enable plasmaprocessing under a low pressure.

In this example, an electric power source 40 supplies electric powerhaving a frequency of 60 MHz. The suscepter 5 as the lower electrode isconnected to a high frequency electric power source 50 via a matchingdevice 51 on the supplying line.

The high frequency electric power source 50 supplies high frequencyelectric power having an arbitrary frequency within a range of 100 kHzto 10 MHz. By applying the electric power within such a frequency band,a suitable ion effect can be applied to the wafer W without any damage.In this embodiment, an electric power source for supplying electricpower having a frequency of 2 MHz is used as the high frequency electricpower source 50.

The process using the plasma etching apparatus 1 constituted as abovewill be described below.

After the gate valve 32 is opened, the wafer W is conveyed to thechamber 2 from the load lock chamber (not shown) to be mounted on theelectrostatic chuck 11. The direct voltage source 13 then applies adirect voltage to electrostatically absorb the wafer W on theelectrostatic chuck 11.

The gate valve 32 is then closed and the exhaust system 35 reduces thepressure in the chamber 2 to the desired level.

Subsequently, the valve 28 is opened to introduce the process gas intothe upper electrode 21 from the process gas source 30 through theprocess gas supplying pipe 27 and the gas inlet 26 while the gas flowrate is controlled by the mass flow controller 29. The process gaspasses through the delivery holes 24 of the electrode plate 23 and isdelivered evenly to the wafer W as indicated by an arrow shown in FIG. 1so as to maintain the pressure in the chamber 2 at a predeterminedvalue.

The high frequency electric power source 40 applies electric powerhaving a high frequency no lower than 27 MHz, for example, 60 MHz, tothe upper electrode 21. By applying the high frequency wave in such amanner, a high frequency electric field is generated between the upperelectrode 21 and the suscepter 5 as the lower electrode. The process gasis dissociated to be plasma in the electric field, and the plasma etchesthe wafer W.

On the other hand, the high frequency electric power source 50 applieselectric power having high frequency within the range of 100 kHz to 10MHz, for example, 2 MHz, to the suscepter 5. By applying the highfrequency wave in such a manner, the ions in the plasma are introducedinto the side of the suscepter 5, and anisotropic property of theetching is improved by the ion assistance.

By setting the frequency of the high frequency electric power applied tothe upper electrode 21 at 27 MHz or higher, the density of plasma can beincreased. However, merely by setting the frequency of the highfrequency electric power applied to the upper electrode at the highlevel, the harmonic is reflected from the plasma. The reflected harmonicgenerates the standing wave under the electrode plate 23, which causesthe unevenness of the electric field under the electrode plate 23.

More specifically, when the high frequency wave of 27 MHz or higher isemployed to generate plasma, a harmonic n times higher than thefrequency of the applied electric power will be easily generated byplasma. When the harmonic backs to the high frequency wave source fromthe upper electrode 21, the harmonic is reflected at the portions suchas a border between the upper electrode 21 and the insulating member 25as indicated as A and B and the electric power supplying positionindicated as C in FIG. 2, and generates the standing wave between theseportions and the center of the upper electrode 21 indicated as D.

When the wavelength of the standing wave equals to ¼ times of awavelength λ of a harmonic, i.e., λ/4, the density of plasma isincreased near the center of the upper electrode 21, which will causeuneven plasma. For example, when a high frequency wave having afrequency of 60 MHz is employed as the high frequency electric powersource 40, the wavelength of the high frequency wave is 5 m. Assumingthat the distance between the portions A to D is set at 0.14 m, thecalculation indicates that the harmonic of the ninth degree will beeasily generated.

In consideration of the wavelength shortening rate proportional to the½th power of the dielectric constant of high frequency wave pathmaterial, the harmonic of the third to sixth degree will be easilygenerated. When the distance between the portions A to D is set at 0.07m, however, the similar problem will occur even using the high frequencywave of 13.56 MHz.

In contrast, according to the present embodiment, the harmonic back tothe high frequency electric power source 40 is absorbed by providing theharmonic absorbing member 51 to the electrode plate 23 on the side ofthe opposing face, thereby the generation of the standing wave can beprevented.

The harmonic absorbing member 51 is formed in a ring-like shape in thepresent embodiment to improve the harmonic absorbing effect. It goeswithout saying that the shape of the harmonic absorbing member 51 is notlimited to a ring. The same effect can be also attained by providing theharmonic absorbing member 51 to the outer periphery of the upperelectrode 21, as shown in FIG. 3.

When the harmonic absorbing member 51 is formed of ferrite sinter, theharmonic absorbing member 51 can absorb and attenuate harmonic using themagnetic resonance loss effect, as described above. In this case, thefrequency band that can be attenuated will be shifted by the thicknessof the harmonic absorbing member 51. When the thickness of the harmonicabsorbing member 51 is halved, the frequency band that can be attenuatedwill be doubled.

More specifically, when the thickness of the harmonic absorbing member51 is 7 mm, the harmonic of 200 to 800 MHz can be attenuated by 20 dB,as shown in FIG. 4. When the thickness of the harmonic absorbing member51 is 4.5 mm, the harmonic of 700 MHz to 3 GHz can be attenuated by 20dB, as shown in FIG. 5. The frequency band that can be attenuated can bewidened by laminating ferrite layers having different frequencycharacteristics. For example, when the above-mentioned layers having athickness of 7 mm and 4.5 mm are laminated, the harmonic having a widefrequency band from 200 MHz to 3 GHz can be attenuated.

The present embodiment will not be limited to the first embodiment andvarious modifications can be attained.

For example, the case where the upper electrode is applied with electricpower having high frequency of 27 MHz is described in the firstembodiment, but the frequency lower than 27 MHz is also effective.

Further, in the present embodiment, the upper and lower electrodes areapplied with electric power having high frequency in the firstembodiment, the type that only the upper electrode is applied withelectric power having high frequency may be employed. The presentembodiment can be applied to the apparatus wherein the lower electrodeis applied with electric power having high frequency. In this case, theharmonic absorbing member is arranged to come into contact with the edgeportion of the face of the lower electrode, which is opposed to theupper electrode, or the periphery of the lower electrode.

In addition, the case where the semiconductor wafer is used as thesubstrate to be processed and etched is described in this embodiment,but the substrate is not limited to the semiconductor wafer, but theother substrate such as a liquid display apparatus (LCD) or the like maybe processed. The plasma processing is not limited to the etching, butan other processing such as sputtering, CVD, or the like may beperformed.

According to the present embodiment, the first electrode is applied withelectric power having high frequency, and the harmonic absorbing memberfor absorbing harmonic having frequency of the high frequency waveelectric power applied by the high frequency wave electric powerapplying means is arranged to come in contact with the edge portion ofthe face of the first electrode, which is opposed to the secondelectrode, or the periphery of the first electrode. With this method,the harmonic reflected by plasma passes through the electrode andreaches the harmonic absorbing member before returning to the highfrequency electric power source, where the harmonic will be absorbed.

Accordingly, the standing wave due to the harmonic will be preventedfrom being generated, and the unevenness of the electric field on thesurface of the electrode, which is caused by the standing wave, can besuppressed to make the density of plasma even.

FIG. 6 shows an example of a constitution of a plasma processingapparatus according to the second embodiment of the present invention,used as a capacitive coupling type parallel plate etching apparatus. Theconstituent elements as the main feature of the apparatus according tothe present embodiment will be described below, and the same constituentelements as those of the first embodiment shown in FIG. 1 will bedenoted by the same symbols and the description thereof will be omitted.

The upper electrode 21 of this etching apparatus 102 is arranged on theupper portion in the chamber 2 to be opposed to a suscepter 5 via aninsulating member 25 covering the electrode like a ring along the outerperiphery thereof. The upper electrode 21 is constituted by theelectrode plate 23 having numerous delivery holes 24 and the electrodesupporting body 22 so as to be integrated.

The upper electrode of the present embodiment does not have the harmonicabsorbing member 51 or the insulating member 52 described in the firstembodiment, but is attached directly to the chamber 2 by the insulatingmember 25. The other structure is the same as that described in thefirst embodiment.

The structure of the upper electrode 21 will be described below indetail.

The electrode 23 of the upper electrode 21 is normally formed of aconductor or semiconductor such as Si, SiC or the like. When thefrequency of the high frequency electric power 40 supplied via theelectric power supplying rod 33 is increased, the skin effect will begenerated to supply electric power only to the surface of the electrode.As shown in FIG. 7, the electric power passes the surface of theelectric power supplying rod 33, the upper surface of the electrodesupporting body 22, the side face of the electrode supporting body 22,and the side face of the electrode plate 23, and reaches the lowersurface of the electrode plate 23, which is a plasma contacting face.

In this case, the electric power supplying rod 33 is connected to thecenter of the non-opposing face of the upper electrode 21, and thus theelectric power has the same phase anywhere in the edge portion on theopposing face of the electrode plate 23. As shown in FIG. 8, theelectric power having the same phase is supplied gradually toward thecenter of the opposing face from the edge portion of the electrode plate23. With this constitution, the phase difference d/λ; (λ; is thewavelength of the electric wave on the electrode, and d is a radius ofthe electrode) is generated between the center and the edge portion ofthe electrode plate 23.

When the frequency of the high frequency electric power applied isincreased, the inductance (LωjΩ) in the direction in which the electrodeplate 23 is opposed to the suscepter 5 is not neglected. The impedanceat the center of the opposing face of the electrode plate 23 will bedecreased due to the interference by the phase difference d/λ, therebythe strength of the electric field of the center of the electrode plate23 is higher than that of the edge portion. The center of the electrodeplate 23 comes in contact with plasma, and thus is an open-circuitterminal of an RF equivalent circuit.

Accordingly, the electric field supplied to plasma is similar to thestanding wave, which causes the unevenness of the density of plasma.

In the first example to solve the unevenness of the density of plasma,the opposing face of the electrode plate 23 is constituted by an outerportion 61 formed of a conductor or semiconductor having a lowresistivity of around 50 mΩ·cm and a central portion 62 formed of adielectric, as shown in FIG. 9. By forming the central portion 62 ofdielectric, the capacitance between the plasma and the dielectric isadded at the portion. The impedance Z will be expressed as follows:

Z=Lω−(1/Cω)j

[where ω=2πf (f: frequency)]The inductance component (Lω) in the direction of the diameter of theelectrode plate 23 in the impedance Z can be thus offset by thecapacitance component (−1/Cω) of the capacitance C of the dielectricmember 62.

Accordingly, the change of the impedance Z due to the phase is preventedalmost perfectly in the opposing face of the electrode plate 23, therebythe electric field strength of the center of the opposing face of theelectrode plate 23 is decreased, which makes the electric field appliedto plasma from the lower face of the electrode even, and the density ofplasma can be also made even.

The diameter of the central portion 62 formed of dielectric ispreferably 10 to 50 mmφ when the diameter of the electrode plate 21 isset at 300 mmφ. The dielectric constant of the dielectric comprising thecentral portion 62 needs to be set merely enough to offset theinductance component Lω, and thus the central portion 62 may be formedfrom a polyimide resin having a dielectric constant of 3, for example.The outer portion 61 can be formed from conductor or semiconductor suchas Si, SiC or the like, which is normally used to form an electrodeplate.

The second example of the upper electrode 21 will be described below.

According to the second example, the electrode plate 23 is constitutedby an outer portion 63 formed of conductor or semiconductor havingrelatively low resistivity of 50 mΩ·cm for example, and a centralportion 64 formed of high resistant member having relatively highresistivity of 1 to 100 Ω·cm, as shown in FIG. 10.

By forming the central portion 64 of such a high resistant member, thethickness of the portion supplied with electric power at the portion,i.e., so-called skin depth δ will be varied. More specifically, the skindepth δ can be expressed as

δ=(2/ωσμ)^(1/2)

[where σ is conductivity, μ is magnetic permeability]When the resistance becomes larger to decrease the conductivity σ, theskin depth δ will become larger.

When the skin depth δ of the high resistance member 64 increases morethan the thickness of the high resistance member 64, the high frequencyelectric power reaches the rear face (non-opposing face) of the highresistance member 64 to be supplied there as shown in FIG. 11. On theway from the rear face to the lower face of the high resistance member64, the high frequency electric power will be discharged as Joule heat.

By virtue of the heat discharge, the electric field strength of thecenter of the opposing face of the electrode plate 23 is made even, asthe result, the electric field applied to plasma from the opposing faceof the electrode plate 23 is made even, and the density of plasma can bealso made even.

The diameter of the central portion of the high resistance member 64 ispreferably 50 to 220 mmφ when the diameter of the electrode 21 is set at300 mmφ. It is preferable that the high resistance member (centralportion) 64 is formed from Si since the resistance can be adjustedmerely by adjusting the amount of the dopant such as boron.

The outer portion 63 can be formed from a conductor or semiconductorsuch as Si, SiC or the like, which is normally used to form an electrodeplate. It is easier to form the entire electrode plate 23 from Si andform the outer portion 63 and the high resistance member 64 by changingthe doping amount of the dopant such as boron.

The third example of the upper electrode 21 will be described below.

According to the present example, a dielectric member 65 is provided tothe electrode plate 23 to come in contact with the center of thenon-opposing face of the electrode plate 23, as shown in FIG. 12. Inthis example, the electrode plate 23 is formed of conductor orsemiconductor having resistivity within 1 to 100 Ω·cm, such that theskin depth δ is larger than the thickness of the electrode plate 23.

By forming the electrode plate 23 in such a manner, the high frequencyelectric power reaches the rear face (non-opposing face) of theelectrode plate 23 to be supplied there. By arranging the dielectricmember 65 on the central portion of the rear surface of the electrodeplate 23, the capacitance between the plasma and the dielectric is addedat the portion.

Accordingly, as in the first example, the inductance component (Lω) inthe direction of the diameter in the impedance Z can be thus offset bythe capacitance component (−1/Cω) of the capacitance C of the dielectricmember 62. The change of the impedance Z due to the phase is thusdecreased in the central portion of the opposing face of the electrodeplate 23, thereby the electric field strength of the center of theopposing face of the electrode plate 23 is decreased, which makes theelectric field applied to plasma from the lower face of the electrodeeven, and the density of plasma can be also made even.

In the third example, the electrode plate 23 need not be divided intotwo portions, unlike the first and second examples, and the conventionalintegrated electrode plate formed of a conductor and semiconductor canbe employed.

The diameter of the dielectric member 65 formed of a dielectric ispreferably 50 to 220 mmφ when the diameter of the electrode 21 is set at300 mmφ. The dielectric constant of the dielectric member 65 needs to beset merely enough to offset the inductance component Lω, and thus thedielectric member 65 may be formed from a polyimide resin having adielectric constant of 3, for example.

The fourth example of the upper electrode 21 will be described below.

According to the present example, a high resistant member 66 is providedto the electrode plate 23 to come in contact with the center of the rearface of the electrode plate 23, as shown in FIG. 13. According to thefourth example, the electrode plate 23 is formed of a high resistantmember having resistivity within a range of 1 to 100 Ω·cm and the skindepth δ is larger than the thickness of the electrode plate 23.

By forming the electrode plate 23 in this manner, the high frequencyelectric power reaches the non-opposing face of the electrode plate 23to be supplied there. By arranging the high resistant member 66 in thecentral portion of the rear face of the electrode plate 23, the highfrequency electric power supplied thereto will be discharged as Jouleheat. By virtue of the heat discharge, the electric field strength ofthe center of the opposing face of the electrode plate 23 is decreased.Accordingly, the electric field applied to plasma from the opposing faceof the electrode is made even, and the density of plasma can be alsomade even. Also in the fourth example, the electrode plate 23 needs notto be divided into two portions, unlike the first and second examples,and the conventional integrated electrode plate formed of conductor andsemiconductor can be employed.

The diameter of the high resistant member 66 formed of dielectric ispreferably 50 to 220 mmφ when the diameter of the electrode 21 is set at300 mmφ. It is preferable that the high resistant member 66 is formedfrom Si since the resistance can be adjusted merely by adjusting theamount of the dopant such as boron.

The fifth example of the upper electrode 21 will be described below.

According to the present example, an insulating layer 67 is provided onthe opposing face of the electrode plate 23, as shown in FIG. 14. Theinsulating layer 67 can be formed by the frame spraying of ceramic orthe like, but can also be formed in other ways. By forming theinsulating layer 67 in this manner, the capacitive coupling is formedbetween plasma and the electrode plate 23 via the insulating layer 67.

In other words, there are a plenty of capacitors between the electrodeplate 23 and plasma in an RF equivalent circuit. As a result, theinductance component (Lω) in the direction in which the suscepter 5 andthe electrode plate 23 are opposed to each other can be thus offset bythe capacitance component (−1/Cω) of the insulating layer 67.

The change of the impedance Z due to the phase is thus prevented almostperfectly on the opposing face of the electrode plate 23, thereby theelectric field applied to plasma from the opposing face of the electrodeis made even, and the density of plasma can be also made even.

The material and the thickness of the insulating layer 67 are determinedsuch that the capacitance of the insulating layer is set high enough tooffset the inductance component (Lω).

The unevenness of the electric field on the opposing face of theelectrode plate 23 of the upper electrode 21 is caused not only by thechange in direction of the inductance on the surface of the electrodewhen the frequency of the electric power applied to the electrode isincreased. The unevenness of the electric field on the opposing face ofthe electrode plate 23 will be caused also in the case where thenon-linear characteristics of plasma remarkably appears, a harmonic ofthe reflection wave from plasma is increased, and the harmonic generatesa standing wave on the surface of the electrode.

More specifically, the reflection wave of the high frequency electricpower from the plasma contains so much amount of harmonics. Theharmonics are further reflected by the inductance component of theelectric power supplying rod 33. Some of the harmonics contain thereflection waves reflected by the rod 33 having a wavelength for formingthe standing wave when the diameter of the electrode 21 is set at 250 to300 mmφ, the standing wave is formed on the opposing face of theelectrode plate 23 to increase the electric field strength in thecentral portion of the surface of the electrode plate 23.

In order to solve the above-mentioned problem, according to the sixthexample of the upper electrode 21, a member 68 having an electromagneticwave absorbing effect, such as ferrite sinter, is provided to theelectrode plate 23 so as to come in contact with the central portion ofthe non-opposing face of the electrode plate 23, as shown in FIG. 15.With use of such a member 68, the harmonic from plasma is absorbed. Byabsorbing the harmonic in this manner, the standing wave can beprevented from being generated, the electric field on the opposing faceof the electrode plate 23 is made even, and the density of plasma can bemade even.

In this case, the member 68 having the electromagnetic wave absorbingeffect is formed from the material having a property that absorbs theharmonic from plasma but does not absorb the frequency of the higherfrequency electric power. The frequency band to be absorbed by themember 68 can be adjusted by the type of material and component.

The above-mentioned first to sixth examples of the upper electrodes inthe second embodiment is effective particularly in the case where thefrequency of the electric power applied to the electrode is 27 MHz ormore, and the density of plasma is as high as 1×10¹¹/cm³ or higher.

Next, the etching apparatus according to the second embodiment will bedescribed about the example in which an oxide film formed on the wafer Wis etched.

As in the first embodiment, the wafer W is transferred into the chamber2 to be electrostatically attached to an electrostatic chuck 11. Afterthe pressure of the chamber 2 is reduced to a predetermined level, theprocess gas is introduced into the chamber 2 to be blown to the wafer Wunder a predetermined pressure.

Subsequently, a high frequency electric power having frequency of 60 MHzis applied to the upper electrode 21 from the high frequency electricpower source 40. By applying such a high frequency electric power, ahigh frequency electric field is generated between the upper electrode21 and the suscepter (lower electrode) 5, and the process gas isdissociated therein to be plasma. On the other hand, the high frequencyelectric power source 50 applies electric power having high frequencywithin the range of 1 to 4 MHz, for example, 2 MHz, to the suscepter 5as a lower electrode. By applying the high frequency wave in such amanner, the ions in the plasma are introduced into the side of thesuscepter 5, and anisotropy of the etching is improved by the ionassistance.

By setting the frequency of the high frequency electric power applied tothe upper electrode 21 at 27 MHz or higher, the density of plasma can beincreased. However, in the conventional constitution of the upperelectrode, the unevenness of the electric field on the opposing face ofthe electrode plate 23 will be caused due to the standing wave, asdescribed before.

According to the present embodiment, any of the causes of the unevennessof the electric field on the opposing face of the electrode plate 23 canbe eliminated by constituting the upper electrode 21 as described in thefirst to sixth examples. Accordingly, the electric field on the opposingface of the electrode plate 23 can be made even more than theconventional one, thereby the density of plasma can be made more even.

More specifically, with the above-mentioned constitution of the upperelectrode, the frequency of the high frequency electric power isincreased, and the problem unique to the case when the density of plasmais increased can be solved, thereby high-density and an even plasma canbe generated.

Therefore, according to the present embodiment, the evenness of theetching can be improved to suitably cope with the downsizing of thedesign rule.

When the frequency of the electric power applied to the electrode is 27MHz or more, and the density of plasma is as high as 1×10¹¹/cm³ orhigher, unevenness will easily occur. The above-mentioned upperelectrode according to the present embodiment is effective particularlyin such a case.

The present embodiment is not be limited to the above-mentionedexamples, and various modifications can be made. For example, the upperand lower electrodes are applied with electric power having a highfrequency, only the upper electrode may be applied with electric powerhaving a high frequency. Further, the case where the upper electrode isapplied with electric power having a high frequency of 27 to 50 MHz isdescribed in the first embodiment, but the frequency is not limited tothis range. In addition, the case where the semiconductor wafer is usedas the substrate to be processed and etched is described in thisembodiment, but the substrate is not limited to the semiconductor wafer,but another substrate, such as a liquid display apparatus (LCD) or thelike, may be processed. The plasma processing is also not limited toetching, but another processing such as sputtering, CVD, or the like maybe performed. The above-mentioned examples of the upper electrodes shownin the present embodiment can be employed together.

FIG. 16 shows an example of a constitution of a plasma processingapparatus according to the third embodiment of the present invention,used as a capacity coupling parallel plate etching apparatus. The sameconstituent elements as those of the first embodiment shown in FIG. 1will be denoted by the same symbols and the description thereof will beomitted.

The etching apparatus 103 is different in that the electrode rod on theside of the upper electrode 21 is removed and the chamber 2 covering therod is formed in a different shape. The upper electrode 21 is connectedto a direct voltage source 43 for boosting a self bias voltage (Vdc) ofthe upper electrode 21 via a low pass filter (LPF) 44 for transmittingonly a direct voltage.

The matching device 41 is provided therein with a capacitor (not shown)connected in series, and thus the high frequency electric power source40 and the direct voltage source 43 will not conflict with each other.

The outer periphery of the upper electrode 21 is provided with aninsulating member 25 formed in a ring-like shape along the periphery.The insulating member 25 is air-tightly attached at the outer peripheralface to the inner sidewall of the chamber 2. With this constitution, theharmonic absorbing member 51 is not provided to the apparatus of thepresent embodiment.

The operation of the plasma etching apparatus 103 constituted as abovewill be described below.

As in the first embodiment, the wafer W is transferred into the chamber2 to be electrostatically attached to the electrostatic chuck 11. Afterthe pressure of the chamber 2 is reduced to a predetermined level, theprocess gas is introduced into the chamber 2 to be blown to the wafer Wunder a predetermined pressure.

Subsequently, high frequency electric power having a frequency of 27 MHzor more, for example, 60 MHz, is applied to the upper electrode 21 fromthe high frequency electric power source 40. By applying such highfrequency electric power, plasma is generated between the upperelectrode 21 and the suscepter 5 to etch the wafer W. On the other hand,the high frequency electric power source 50 applies electric powerhaving a high frequency of 2 MHz, for example, to the suscepter 5, andan etching with excellent anisotropy by ion assistance is performed.

Also in the present embodiment, the unevenness of the electric fieldwill occur on the opposing face of the electrode plate 23, as in thefirst embodiment.

More specifically, when the high frequency electric power is appliedonly by the high frequency electric power source 40, the harmonic fromthe plasma generates a standing wave on the opposing face of the upperelectrode 21, and an unevenness of the electric field will occur on theopposing face of the upper electrode 21. When the frequency of the highfrequency electric power applied to the upper electrode is increased to27 MHz or higher, the self bias voltage (Vdc) of the upper electrode 21is decreased thereby. As a result, the thickness of the entire plasmasheath S of the upper electrode 21 will be decreased as shown in FIG.17A. Due to the unevenness of the electric field by the standing wave,the plasma sheath of the central portion of the electrode will befurther decreased in thickness. The change ratio of the thickness of theoverall portion of the plasma sheath is increased in such a manner, andthe self bias voltage (Vdc) on the surface of the upper electrode 21will be made uneven. As a result, the evenness of plasma will bedeteriorated.

In contrast, by applying a high frequency electric power having afrequency higher than 27 MHz to the upper electrode 21 from the highfrequency electric power source 40 and applying a direct voltage fromthe direct voltage source 43, the self bias voltage (Vdc) will beincreased by the valve of the direct voltage as shown in FIG. 17B. Theincreased voltage S1 forms a thicker plasma sheath S′, which cansuppress the influence of the unevenness of the self bias voltage (Vdc)and the plasma sheath.

With this method, even if the unevenness occurs in the plasma density,the influence thereof will be suppressed at the minimum level, and theetching rate can be regarded to be even in the practical level.

For example, when high frequency electric power of 60 MHz and 1 kW isapplied to the upper electrode 21 from the high frequency electric powersource 40, the relationship Vdc=−100 V will be attained. Assuming thefluctuation of Vdc is around ±10 V, the fluctuation rate will be aslarge as ±10%, which will deteriorate the evenness of plasma.

However, when a direct voltage of −400 V, for example, is applied fromthe direct voltage source 43, the total sum of the self bias voltage(Vdc) will be increased to −(100+400)±10 V. As a result, the fluctuationrate will be decreased to ±2%, and the evenness of Vdc will be improved.The evenness of plasma can be considered to be also improved thereby.

The fourth embodiment of the present invention will be described below.

FIG. 18 shows an example of a constitution of a plasma processingapparatus according to the fourth embodiment of the present invention,used as a capacity coupling parallel plate etching apparatus. The sameconstituent elements as those of the second embodiment shown in FIG. 16are denoted by the same symbols and the description thereof is omitted.

In the etching apparatus 104, the upper electrode 21 is connected to twohigh frequency electric power sources. One is the first high frequencyelectric power source 70 for generating plasma connected to the upperelectrode 21 via a high pass filter (HPF) 72 and a matching device 71.The other is the second high frequency electric power source 73connected to the upper electrode 21 via a low pass filter (LPF) 75 and amatching device 74.

The first high frequency electric power source 70 has a high frequencyof 27 MHz or higher. By applying electric power having such a highfrequency, suitably dissociated and high-density plasma can be generatedin the chamber 2, thereby the plasma processing under a low pressure canbe attained. In this example, the first high frequency electric powersource 70 outputting high frequency electric power of 60 MHz isemployed.

The second high frequency electric power source 73 outputs highfrequency electric power of a frequency lower than that output from thefirst high frequency electric power source 70, preferably, 2 to 10 MHz.In the present embodiment, the second high frequency electric powersource 73 outputting high frequency electric power of 2 MHz is employed.

More specifically, the second high frequency electric power source 73outputs the high frequency electric power of a frequency lower than thatoutput from the first high frequency electric power source 70, and thusfunctions to boost the self bias voltage (Vdc) of the upper electrode21.

The high pass filter (HPF) 72 is intended to cut the current having afrequency equal or lower than the frequency of the second high frequencyelectric power source 73, and the low pass filter (LPF) 75 is providedto cut the current having a frequency equal to or higher than thefrequency of the first high frequency electric power source 70.

The plasma etching apparatus 104 constituted as above performs theetching process in basically the same manner as using the plasma etchingapparatus 103 according to the third embodiment.

At this time, the density of plasma can be increased by setting thefrequency of the high frequency electric power applied to the upperelectrode 21 at 27 MHz or higher. However, merely by increasing thefrequency, the standing wave is generated on the opposing face of theelectrode plate 23 by a harmonic due to the reflected wave from theplasma, which will cause unevenness of the electric field on theopposing face of the electrode plate 23.

Instead of the application of the direct voltage according to the thirdembodiment, according to the fourth embodiment, the second highfrequency electric power source 73 applies the high frequency electricpower having a frequency lower than the frequency of the first highfrequency electric power source 70 to the upper electrode 21.

The self bias voltage generated by the high frequency electric powerapplied by the second high frequency electric power source 73 is largerthan the self bias voltage generated by the high frequency electricpower applied by the first high frequency electric power source 70.Therefore, the high frequency electric power from the first and secondhigh frequency electric power sources 70 and 73 overlap, as a result, aremarkably high self bias voltage (Vdc) of the upper electrode 21 can beattained compared with the case where a high frequency electric power isapplied to the electrode only from the first high frequency electricpower source 60, as indicated in the embodiment described before. Theincreased voltage forms a thicker plasma sheath, which can suppress theinfluence of the unevenness of the self bias voltage (Vdc) and theplasma sheath, as in the case shown in FIG. 17( b).

With this method, the plasma density can be made even, on a practicalbasis, and the etching rate can be made even.

In an example where high frequency electric power of 60 MHz and 1 kW isapplied to the upper electrode 21 from the high frequency electric powersource 70, the relationship Vdc=−100 V will be attained. Assuming thefluctuation of Vdc is around ±10 V, the fluctuation rate will be aslarge as ±10%, which will deteriorate the evenness of plasma. However,when a high frequency electric power of 2 MHz and 500 W, for example, isapplied to the upper electrode 21 from the second high frequencyelectric power source 73, the self bias voltage (Vdc) generated by thesecond high frequency electric power source 73 will be increased toaround −400 V, and the total sum of the self bias voltage (Vdc)generated by the second high frequency electric power source 73 will beincreased to −(100+400) V±10 V. As a result, the fluctuation rate willbe decreased to ±2%, and the evenness of Vdc will be improved. Theevenness of plasma can be also improved thereby.

The fourth embodiment is not be limited to the above-mentioned examples,and various modifications can be made.

For example, the upper and lower electrodes are applied with electricpower having a high frequency, only the upper electrode 21 may beapplied with electric power having a high frequency.

Further, where the oxide film formed on the wafer is etched using thesemiconductor wafer, the present embodiment can be applied to an etchingfor an insulating film other than the oxide film, a polysilicon film,and the like. In addition, the substrate to be processed is not limitedto the semiconductor wafer, and another substrate, such as a liquiddisplay apparatus (LCD) or the like may be processed.

FIG. 19 shows an example of a constitution of a plasma processingapparatus according to the fifth embodiment of the present invention,used as a capacitive coupling type parallel plate etching apparatus. Thesame constituent elements as those of the first embodiment shown in FIG.1 will be denoted by the same symbols and the description thereof willbe omitted.

The etching apparatus 105 is constituted to have an electromagnetic waveshielding box 80 for shielding electromagnetic waves above thenon-opposing face of the upper electrode 21 in the chamber 2.

In this constitution, the electric power supplying rod 33 for supplyinghigh frequency electric power output from the high frequency electricpower source 40 is connected to the electrode supporting body 22 of theupper electrode 21.

There is provided above the electrode supporting body 22 with aconductive plate-like member 82. A cylindrical member 81 and plate-likemember 82 are electrically connected with each other, and the plate-likemember 82 is connected to the grounded chamber 2.

More specifically, the cylindrical member 81 and the plate-like member82 are grounded via the chamber 2. The cylindrical member 81 candecrease the inductance of the electric power supplying rod 33 as willbe described later, and also ground the harmonics. The plate-like member82 can also decrease the inductance of the upper electrode 21, and alsoground the harmonics.

The other constituent elements are the same as those described in thefirst embodiment.

The operation of the plasma etching apparatus 105 constituted as abovewill be described below. In this embodiment, the etching of the filmformed on the wafer W will be described.

As in the first embodiment, the wafer W is transferred into the chamber2 to be electrostatically attached to electrostatic chuck 11. After thepressure of the chamber 2 is reduced to a predetermined level, theprocess gas is introduced into the chamber 2 to be blown to the wafer Wunder a predetermined pressure.

Subsequently, high frequency electric power having a frequency of 27 MHzor more, for example, 60 MHz, is applied to the upper electrode 21 fromthe high frequency electric power source 40. By applying such a highfrequency electric power, plasma is generated between the upperelectrode 21 and the suscepter 5 to etch the wafer W. On the other hand,the high frequency electric power source 50 applies electric powerhaving a high frequency of 2 MHz, for example, to the suscepter 5, andan etching with excellent anisotropy by ion assistance is performed.

In general, the density of plasma can be increased by increasing thehigh frequency electric power applied to the upper electrode 21 to 27MHz or higher, as described before. However, the inductance of theelectric power applying rod is very large, and thus the harmonic isreflected from the plasma by the inductance component of the electricpower applying rod. The reflected harmonic is further reflected by thefaces of the electromagnetic wave shielding box 80, and returns to theopposing face of the upper electrode 21 generating the plasma.Particularly with an electrode having a diameter of 250-300 mmφ, astanding wave will be easily generated on the surface of the electrodedue to the harmonic, which makes the electric field on the electrodeuneven.

In contrast, according to the present embodiment, the conductivecylindrical member 81 is arranged near the electric power supplying rod33. This constitution is equivalent to a circuit having a number ofcapacitors arranged in parallel between the cylindrical member 81 andthe electric power supplying rod 33, as shown in FIG. 20. The inductancecomponent of the electric power supplying rod 33 is cancelled by thecapacitance component of the capacitors to decrease the impedance, withthe result that the inductance component of the electric power supplyingrod 33 will be decreased.

The cylindrical member 81 is grounded via the chamber 2, and thus theharmonic reflected by the electric power supplying rod 33 will begrounded through the cylindrical member 61.

Accordingly, the harmonic from plasma will not be easily reflected bythe electric power supplying rod 33, and the harmonic itself will bedecreased, with the result that a standing wave generated by thereflection of the harmonic will not be easily generated on the plasmacontacting face (opposing face) of the electrode plate 23.

Consequently, the electric field on the plasma contacting face of theelectrode plate 23 can be made more even, which makes the plasma densityeven.

The inductance component on the non-opposing face of the electrodesupporting body 22 will contribute to generate a standing wave due tothe reflection of the harmonic. However, according to the presentembodiment, the plate-like member 82 is arranged near the non-opposingface of the electrode supporting body 22, which is equal to theequivalent circuit having a number of capacitors arranged in parallelbetween the electrode supporting body 22 and the plate-like member 62,as shown in FIG. 21. The inductance component at the portion will bedecreased, according to the same principle as mentioned above. Theharmonic will be grounded through the plate-like member 82.

Accordingly, the plate-like member 82 will further improve the standingwave preventing effect.

The distance between the cylindrical member 81 and the electric powersupplying rod 33, and the distance between the plate-like member 62 andthe electrode supporting body 22 need to be set suitably in accordancewith the capacitance necessary for canceling the standing wave. Forexample, when the high frequency electric power is set at 2 kW, thedistances need to be set at 8 mm or more to prevent the breakdown inair.

In point of view of forming the capacitors, no component needs to beprovided between the cylindrical member 81 and the electric powersupplying rod 33, and the distance between the plate-like member 62 andthe electrode supporting body 22. However, if the filtering functionneeds to be improved, an electric wave absorbing body may be providedtherebetween. Similarly, if the dielectric constant needs to beadjusted, a dielectric such as a fluoroplastic (trade name: Teflon) maybe provided.

FIG. 22 shows an example of a constitution of a plasma processingapparatus according to the sixth embodiment of the present invention,used as a capacitive coupling type parallel plate etching apparatus. Thesame constituent elements as those of the first embodiment shown in FIG.1 are denoted by the same symbols and the description thereof isomitted.

In the etching apparatus 106, an electric power supplying rod 93 isarranged at a position shifted from the central portion of thenon-opposing face of the upper electrode 21 so as to supply electricpower. According to the fifth embodiment, the electric supplying rod 93is arranged at the central portion of the non-opposing face of the upperelectrode 21.

There is further provided to the non-opposing face of the upperelectrode 21 with an LC circuit 94 in the opposite side of the positionof the electric supplying rod 93. The LC circuit 94 functions to adjustthe phase of the voltage and current of the high frequency electricpower supplied to the upper electrode 21.

The LC circuit 94 is constructed by a coil 95 capable of varying aninductance and a capacitor 96 capable of varying a capacitance, andconnected in series between the upper electrode 21 and the chamber 2.

There is provided a conductive cylindrical member 91 near the electricpower supplying rod 93 and a conductive plate-like member 92 near theupper portion of the electrode supporting body 22. The cylindricalmember 91 and the plate-like member 92 are electrically connected witheach other, and the plate-like member 92 is electrically connected tothe grounded chamber 2.

The other constituent elements are the same as those described in thefirst embodiment.

The plasma etching apparatus 106 constituted as above performs a similaretching process to that performed by the plasma etching apparatus 105.

However, when the high frequency electric power applied to the upperelectrode 21 is increased to 27 MHz or higher, a standing wave will begenerated for the same reason as described before, and unevenness of theelectric field on the electrode will occur thereby.

When the electric power supplying rod 33 is arranged in the center ofthe upper electrode 21, the phase difference d/λ; (λ; is the wavelengthof the electric wave on the electrode, and d is a radius of theelectrode) is generated between the center and the edge portion of theelectrode plate 23, as shown in FIGS. 7 and 8 before.

In the equivalent electric circuit, the electric power applied to theouter portion of the upper electrode 21 is grounded via an insulator inparallel with the direction in which electric power is supplied to theplasma, and terminated at characteristic impedance (50Ω), and thus theelectric field strength Eo at the outer portion is expressed as

Eo=E·cos(ωt)

The electric field strength Eo at the central portion of the upperelectrode 21 is expressed as

Ec=E·cos(ωt+d/λ)

where λ is the (wavelength shortening) wavelength of the high frequencyelectric power applied to the electrode and harmonic generated by thereflection from plasma, and the high frequency electric power viaplasma.

In this time, the high frequency electric power is gradually supplied tothe central portion from the outer portion, and thus the voltage and thecurrent will be concentrated at the central portion from the outerportion in the electrode plate 23. When the frequency of the highfrequency electric power is increased, the inductance in the directionin which the electrode plate 23 is opposed to will become too large tobe neglected. The impedance at the center of the opposing face of theelectrode plate 23 will be decreased due to the interference by thephase difference.

Due to the above-mentioned problems, the strength of the electric fieldof the center of the electrode plate 23 is higher than that of the edgeportion. The center of the electrode plate 23 comes in contact withplasma, and thus is an open-circuit edge of an RF equivalent circuit.Accordingly, a standing wave having a wavelength λ=2d is generated onthe opposing face of the electrode plate 23, which causes unevenness ofthe density of plasma.

In order to prevent a standing wave generated due to the above-mentionedproblems, according to the present embodiment, high frequency electricpower is supplied to the position shifted from the central portion tothe outer portion of the upper electrode 21 via an electric powersupplying rod 93, and an LC circuit 94 as phase adjusting means isprovided opposite the electric power supplying rod 93 on thenon-opposing face of the upper electrode 21 with respect to the center.By constituting the apparatus in this manner, the phases of the voltageand the current of the high frequency electric power supplied to theupper electrode 21 are made uneven on the outer periphery.

More specifically, by supplying high frequency electric power to theposition shifted from the central portion to the outer portion of theupper electrode 21, the concentration of the voltage and current pathson the opposing face of the electrode plate 23 is prevented. Thereafter,the phases of the voltage and the current of the high frequency electricpower supplied to the upper electrode 21 can be made uneven on thecircumference of the electrode plate 23 by adjusting the inductance ofthe coil 95 and the capacitance of the capacitor 96 by using the LCcircuit 94 so as to shift the phases of the voltage and the current. Bymaking the phases uneven, a standing wave which will be caused by theelectric power supplied from the center of the electrode to the opposingface of the electrode plate 23 can be prevented.

Accordingly, the electric field on the opposing face, i.e., the plasmacontacting face of the electrode plate 23, can be made more even,thereby the evenness of the plasma density can be attained.

The apparatus of the present embodiment is provided with the cylindricalmember 91 and the plate-like member 92, similarly to the firstembodiment, and thus the standing wave due to the reflection of aharmonic cannot be easily generated on the plasma contacting face(opposing face) of the electrode plate 23, and thus the electric fieldon the plasma contacting face of the electrode plate 23, can be mademore even.

The above-mentioned advantage can be attained at a predetermined levelif the electric power supplying rod 93 is shifted more or less from thecenter of the upper electrode 21. However, when the electrode has adiameter of 250 mm, it is preferable to shift 60 mm or more the electricpower supplying rod 93 from the center of the upper electrode 21.

In any of the fifth and sixth embodiments, the higher the frequency ofthe electric power applied to the electrode, the easier the standingwave is generated. The inventions are thus useful particularly in thecase where the frequency of the electric power is 27 MHz or higher. Ifthe frequency of the electric power used is lower than 27 MHz, however,it cannot be said that there is no influence of the standing wave, andthus the present invention will attain a level of advantage.

Similarly, when the density of plasma is as high as 1×10¹¹/cm³ orhigher, the unevenness will easily occur. The above-mentioned upperelectrode according to the present embodiment is effective particularlyin such a case.

The fifth and sixth embodiments can be employed to attain even betterevenness of the density of plasma.

The present embodiment will not be limited to the above-mentionedexamples, and various modifications can be made.

For example, the upper and lower electrodes are applied with electricpower having a high frequency, only one of the electrodes may be appliedwith electric power having a high frequency.

Further, the case where the upper electrode is applied with electricpower is described in the present embodiment, but can be applied to thelower electrode. In addition, the case where the semiconductor wafer isused as the substrate to be processed and etched is described in thisembodiment, but the substrate is not limited to the semiconductor wafer,and other substrates, such as a liquid display apparatus (LCD) or thelike, may be processed. The plasma processing is also not limited toetching, and other processings such as sputtering, CVD, or the like maybe performed.

INDUSTRIAL APPLICABILITY

The plasma processing apparatus according to the present invention usprovided with a harmonic absorbing member for absorbing harmonic havingfrequency of the high frequency wave electric power applied by the highfrequency wave electric power applying means is arranged to come incontact with the electrode. The harmonic absorbing member absorbs theharmonic before returning to the high frequency electric power source. Astanding wave due to the harmonic is prevented from being generated, andthe density of plasma is even.

Further, the plasma processing apparatus according to the presentinvention has two high frequency electric power sources. When highfrequency electric power having a frequency higher than 27 MHz isapplied to the electrode for generating plasma from one of the highfrequency electric power sources, the high frequency electric powerhaving a lower frequency than that of the above electric power isapplied from the other one of the power sources, thereby the self biasvoltages (Vdc) generated by the power sources overlap, to attain a highlevel self bias voltage. By the increased self bias voltages (Vdc) theplasma sheath is made thicker, which can suppress the unevenness of theplasma sheath due to the unevenness of the self bias voltage (Vdc). As aresult, evenness can be attained of the plasma density, and the etchingrate can be made even when the apparatus is used for etching.

1. A plasma processing apparatus comprising: a chamber configured to bemaintained at a reduced pressure; a first electrode and a secondelectrode arranged to be opposed to each other in the chamber, wherein:a substrate to be processed is held on an opposing face of the secondelectrode, and the first electrode has an electrode plate arranged to beopposed to the second electrode, the electrode plate having an outerportion constituted by a conductor or semiconductor and a centralportion constituted by a dielectric member or a high resistance memberwith higher resistivity than that of the outer portion; a process gassource connected to the chamber, and a high frequency electric powersource configured to provide high frequency electric power from a faceof the first electrode to which the second electrode is opposed in orderto form a high frequency electric field between the first and the secondelectrodes to generate a plasma of the process gas, wherein apredetermined plasma processing is performed on the substrate to beprocessed with the plasma.
 2. The plasma processing apparatus accordingto claim 1, wherein the central portion of the electrode plate is formedof a high resistance member such that a skin depth δ expressed by thefollowing formula is larger than the central portion of the electrodeplate in thickness:δ=(2/ωσμ)^(1/2), where ω=2πf (f is frequency), σ is conductivity, and μis magnetic permeability.
 3. The plasma processing apparatus accordingto claim 2, wherein: both the outer portion and the central portion ofthe electrode plate are formed from silicon (Si), and the outer portionhaving low resistivity and the central portion having high resistivityare formed by differentiating doping amounts of dopant into the outerportion and the central portion.
 4. The plasma processing apparatusaccording to claim 1, wherein a frequency of the high frequency electricpower applied to the first electrode by the high frequency electricpower source is 27 MHz or higher, and a density of formed plasma is1×10¹¹/cm³ or higher.